1. Technical Field of the Invention
The present invention relates to an electrophotographic copying apparatus arranged for copying an image by exposing the image by a scanning system.
2. Brief Description of the Prior Art
In an electrophotographic copying apparatus, an electrostatic latent image is first formed by exposing an image, on a photoconductive drum by slit exposure and then transferring a toner image onto a sheet of copy paper after developing the image by a toner development. The transferred paper is then transported to a fixing unit for undergoing a fixing procedure by pressure and heat on the toner image transferred, and thereafter, the paper is discharged.
One the photoconductive drum, cleaning is being carried out even after transferring is finished for removing residual toner which remains thereon. At the fixing unit, cleaning is also carried out in order to prevent the offset phenomenon whereby the image is transferred again to another portion of the transfer sheet since softened and melted toner is stuck to a fixing roller which contacts the surface of the transfer sheet carrying toner image thereon.
A Japanese Published Unexamined Patent Application No. 78072/1982, for instance, discloses a device which is arranged to remove toner stuck to a fixing roller and the like of a copy machine. The device is designed to wind a cleaning web around a supplying roller which is pressed on a roller to be cleaned and then the cleaning web is rolled up successively by a take-up roller. The take-up roller is driven by a separate motor for a predetermined period of time corresponding to a movement of a copying machine and the quantity of cleaning web delivered corresponds with a movement of the copying machine.
The device which has the same structure as described above will be explained with reference to FIGS. 1 and 2.
The cleaning web 101 which is wound around a web roller 102 is rolled up by a take-up roller 104 over a pressure roller 103, and the toner stuck to a fixing roller 100 is removed by pressing the cleaning web 101 to the fixing roller 100 by the pressure roller 103. The pressure roller 103 and the take-up roller 104 are rotatably driven by a driving motor 105 through a series of gears 106. In order to pervent the cleaning web 101 from loosening, the circumferential velocity of the takeup roller 104 is arranged to be faster than that of the pressure roller 103, and a sliding mechanism such as torque limiter 107 is provided at one end of the roller 104 since the circumferential velocity increases corresponding to the increased thickness of the cleaning web 101 being rolled up.
At the other end of the take-up roller 104, one way clutch 108 is provided to prevent the cleaning web 101 from reverse movement. The web roller 102 is freely rotatable and brake is applied by a brake plate 109 biased by a torsion spring 109a provided for preventing the cleaning web 101 from loosening.
With the structure described above, cleaning the surface of the fixing roller 100 is carried out by its rotation in close contact with the cleaning web 101, which is driven by the driving motor 105 for a predetermined period of time corresponding to a movement of a copying machine. The fixing roller 100 is thus cleaned always by a new portion of the cleaning web 101. However, in the structure described above, a separate driving motor 105 is required for moving the cleaning web 101, and as a consequence, it becomes necessary to provide a control device to actuate the driving motor 105 corresponding to the movement of copying operation, thus increasing the cost of the apparatus because of the necessity of providing many expensive component parts.